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  • 1
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: 4B9A is a focusing and monochromatic photon beam at the BSRF, which was constructed in 1990. During the second phase of the BSRF program, the surface of the cylindrical mirror has been coated with Pt, covering the original Ni, and the monochromator has been upgraded. The maximum photon energy extends to 11 keV and the intensity has increased about tenfold with respect to the previous intensity at 6 keV. Synchrotron X-ray diffraction patterns for the Hg-1223 (HgBa2Ca2Cu3O8+δ) superconducting bulk and thin film have been measured at 1.54014 Å. Results indicate that the bulk and film can be indexed as possessing tetragonal symmetry; lattice parameters a = 3.856 Å and c = 15.851 Å for the bulk Hg-1223 compound, and a = 3.8517 Å and c = 15.8511 Å for the film. Their structures are similar.
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 545-547 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The oxide superconductor Bi1.7Pb0.3Sr2−xAgxCa2Cu3Oy has been synthesized under the ordinary pressure. The x-ray diffraction spectra of these specimens show the presence of only 2212 phase when x〈0.4, and the transition temperature achieved 99 K. With the x increase, the structure of sample transfers to 2223 phase. The investigation indicates that substitution of Sr2+ by Ag1+ increases the distance between layers. This may respond to Tc increase in 2212 phase and 2223 phase form at a relatively low temperature. © 1995 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is proposed according to which critical current density Jc at various temperatures T and dc fields B is estimated on (Tl0.5Pb0.5)(Ba0.2Sr0.8)2Ca2Cu3Oy based upon the flux diffusion barrier heights U(J,B,T) determined by means of ac susceptibility measurement at different ac field amplitudes, frequencies, T, and B. Jc is also estimated by the dc hysteresis measurement and compared with the former. The high Jc(B,T) and Tc show that this Tl-based superconductor is one of the more promising high-Tc materials from a practical standpoint. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1671-1675 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time and field sweep rate dependencies of magnetization in high temperature superconductors are derived from a combined view based on the thermally activated flux creep. The τ0 in the magnetization relaxation expression M=M0+M1 ln(1+t/τ0) is a macroscopic quantity related primarily to the sample geometry and other experimental conditions via the effective activation energy U(J0). This activation energy provides an alternative interpretation to the nearly inverse proportionality of τ0 to the field sweep rate. The values of τ0 in the magnetization relaxation of single crystal YBa2Cu3O7−δ are consistent with the calculated ones. As the nonlinear U(J) is taken into account, the curvature in the ||M||-ln t plot may change from negative to positive over a sufficiently long time window, and the magnetization hysteresis M(H) depends on the field sweep rate H(overdot) by const+A ln H(overdot)+B ln2 H(overdot), where A is slightly larger than M1 and B(approximately-greater-than)0. A discussion of the temperature dependency of the normalized flux creep rate is at the conclusion of the article.
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  • 5
    ISSN: 1572-9605
    Keywords: twin domains ; YBCO ; Co-doping ; twin boundary ; model ; electron diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The existence of twin domains in YBa2(Cu1−x Co x )3O y samples was confirmed by many experiments. However, the physical picture of the twin domains has not been reported up to now. By analyzing oxygen content, Cu and Co valences, and Co coordination in those samples, we propose a domain model, which consists of two pairs of parallel zigzag Co-O chains surrounding orthorhombic cells, one along (110) direction and the other along (110) direction. The zigzag Co-O chains are the twin walls, with neighboring walls perpendicular and the opposite ones parallel. The distance between parallel walls (i.e., zigzag Co-O chains) depends upon Co concentration of sample. The twin domain model predicts the geometry, size, and absence of systematic symmetry of the domains. The model also predicts the modulation periodicity of electron diffraction patterns, which depends on Co concentration. All the predictions by the model agree well with the experimental results reported in literatures. Furthermore, the model indicates the possible existence of two domains, which have incommensurable modulation periodicity.
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  • 6
    ISSN: 1572-9605
    Keywords: Thin films ; magnetization ; pinning force ; flux creep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Magnetization measurements have been performed onc-axis oriented Y- and Gd-based superconductive films in a wide range of the temperaturesT (4.2–85 K) and magnetic fieldsH (0–8 T) withH∥ c-axis. The influence of flux creep on both the temperature dependence of critical current densityJ cm and the scaling behavior of flux pinning forceF p has been discussed in detail. The experimental results show that Y and Gd films have different pinning mechanism. Flux pinning-force peaks in high fields are observed in Gd film at high temperatures and can be considered as evidence for collective pinning.
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  • 7
    ISSN: 1572-9567
    Keywords: density ; dielectric constant ; nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new equation for determining the density of nonpolar substances based on measurements of dielectric constants is presented. Applying the new equation to nitrogen at a density from 1 to 30 mol·L−1, the mean deviation of the results calculated from the equation is of the order of 10−4, which is the same as the uncertainty of the experimental data. Owing to its analytical form, the derived equation can be applied to indicate the density of nonpolar substances with a densitometer, without adding error to the experimental uncertainty. This equation is also capable of determining the mean polarizabilities and molecular diameters, which agree well with results from other investigators. We suggest that the equation derived here can be applied to some other nonpolar substances as well.
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  • 8
    ISSN: 1572-9605
    Keywords: Field distribution ; type II superconductor ; cylindrical shape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The self-field effects $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B'}$$ of bulk magnetization current are considered when the applied field $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B} _a$$ is parallel to the rotation axis of a cylinder-shaped type-II superconductor with limited axial length L and radius R, and by using finite-element analysis in a self-consistent way, the field-dependent magnetization current density function $$J_m (|B|)[\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B} (\rho ,z) = \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B} _a + \overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {B'} (\rho ,z)]$$ , the current density, and the field distributions are derived from magnetic moment hysteresis loop m(B a) for the superconductor with full field penetration. When B a≫B p, the average field inside the cylinder $$\left\langle B \right\rangle = \mu _0 [H_a + f_c (L/2R)M]$$ in the Bean model approximation, and the function f c(L/2R) is quantitively given for arbitrary parameter L/2R, where B a=μ0 H a and M=m/(πR 2 L). In addition, the influences of the self-field on the measured m(B a) loop are discussed.
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  • 9
    ISSN: 1572-9605
    Keywords: V-t curve ; I c measurement ; Ag-Bi2223 tapes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Based on the collective creep model, we numerically studied evolution of electric field and current density in superconductors and its influence on transport measurements of critical current. It is shown that many experimental facts, such as the dependence of V-I curves on sweeping rate of applied current and voltage relaxation are the results of this evolution. The simulation results are confirmed by electric transport measurements on Ag-sheathed Bi2−x Pb x Sr2Ca2Cu3O y tapes. Discussions on influences of the voltage relaxation on electric transport measurements including superconducting critical current are made.
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: HgBa2Ca2Cu3O8+δ (Hg-1223) superconducting thin films of about 0.3 μm in thickness have been successfully synthesized. The process involves depositing films (∼ 1 μm thickness) of Ba2Ca2Cu3Ox on a SrTiO3 substrate by pulse laser ablation technique and implanting mercury ions into this deposited film, followed by annealing at oxygen atmosphere. The films so obtained show a relatively wide superconducting transition temperature up to 118 K, as determined magnetically, which is similar to that of underdoping bulk Hg-1223. © 1996 American Institute of Physics.
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